dabbrev problem...

[cons]

I really like and use the dabbrev feature of copying the following
words with SPC M-/ SPC M-/ ... etc. So much infact that I want to do a
command that saves me that extra SPC-press. Basically, the command
should just execute 'dabbrev-expand' if there is a SPC before point,
or else insert a SPC and then execute 'dabbrev-expand':

(defun complete-further (arg)
  "Insert space if necessary and then call dabbrev-expand."
  (interactive "*P")
  (if (not (eq (preceding-char) ?\s))
                (insert ?\s))
  (dabbrev-expand arg))

The only problem is that it ain't working :(

What am I doing wrong?

Best regards,

/Stefan